A basic semiconductor circuit, known as an inverter, includes a p-type MOSFET (PMOS) coupled with an n-type MOSFET (NMOS). An input is coupled to the gate of both the PMOS and the gate of the NMOS, and an output is coupled to a drain of the PMOS and a drain of the NMOS.
Conventionally, the gate of the NMOS is fabricated by first forming an insulating layer(s) above an n-channel region of the NMOS and then forming a NMOS metal gate region above the insulating layer(s). Likewise, the gate of the PMOS is fabricated by first forming an insulating layer above a p-channel region of the PMOS and then forming a PMOS metal gate region above the insulating layer(s). Typically, the same insulating layer(s) is shared by both the PMOS and the NMOS, and the NMOS metal gate region and PMOS metal gate region are adjacent to each other.
The NMOS metal gate region may include a NMOS barrier layer, one or more NMOS work function layers and a NMOS metal gate layer. The NMOS barrier layer surrounds the NMOS work function layers and the NMOS metal gate layer. Likewise, the PMOS metal gate region includes a PMOS barrier layer, one or more PMOS work function layers and a PMOS metal gate layer. The PMOS barrier layer surrounds the PMOS work function layers and the PMOS metal gate layer.
The NMOS work function layers and PMOS work function layers differ in composition. Depending on the particular configuration (e.g., composition) of work function layers, the threshold voltage associated with the NMOS or the PMOS may differ. Because of the close proximity between the NMOS metal gate region and the PMOS metal gate region, cross-diffusion between the work function layers and metal gate layers of the NMOS metal gate region and PMOS metal gate region may occur leading to unwanted shifts in threshold voltages for either the NMOS or the PMOS.
One approach for reducing cross-diffusion between the metal gate regions of the NMOS and PMOS is to increase the distance between the metal gate regions of the NMOS and PMOS. Another approach for reducing cross-diffusion between the metal gate regions of the NMOS and PMOS is to increase the thickness of the NMOS barrier layer and PMOS barrier layer.
New approach for reducing cross-diffusion between the metal gate regions of the NMOS and PMOS would be desirable.